The role of prostaglandin as gastric protective agent will be examined. The morphological basis by which this drug alters or minimizes the effect of necrotizing agents will be evaluated. It has been noted that prostaglandin does not prevent damage to the gastric mucosa but minimizes hyperemia and hemorrhage. The differentiation and proliferation of gastric mucous cells after superficial erosion of the mucosa will be studied. There is increased mitotic activity during regeneration of the mucosa and subsequent differentiation of parietal and chief cells. Further work will be done on the immunolabeling of alpha actinin, myosin, actin, and tubulin in gastric mucous cells by light and electron microscopy.